This invention relates to fluoropolymer compositions which contain a tetraalkylammonium halide, certain polyhydroxy crosslinking agents, and quaternary phosphonium compounds that show improved adhesion to metal when cured.
Fluoroelastomer compositions that are copolymers of vinylidene fluoride with other fluorinated monomers, such as hexafluoropropylene and/or tetrafluoroethylene, when cured with a crosslinking agent, such as bisphenol AF (4,4'-hexafluoroisopropylidene diphenol), and an accelerator, such as benzytriphenylphosphonium chloride, have been used for a variety of applications, including shaft seals. A major problem encountered with these fluorelastomers is their lack of developing sufficiently good adhesion to metal when cured. For example, when these fluoroelastomers are used in fabricating shaft seals, there is a need for enhanced adhesion of the elastomers to the metal portion of the shaft seal assembly. To increase the adhesiveness of these elastomers to metal, the fluoroelastomer copolymers described above have been blended with copolymers of vinylidene fluoride and chlorotrifluoroethylene. Unfortunately, the cure rate of the fluoroelastomer is decreased in the presence of relatively small amounts of copolymers of vinylidene fluoride and chlorotrifuloroethylene.